Extrusion system comprising a screw changing device

ABSTRACT

At least one screw of a screw-type extruder drive-connected via a coupling to a gearing that is driven by a motor, the coupling being able to be coupled to and decoupled from the screw. A gearing carriage is provided which is configured such that the gearing can be drawn by a short distance on the gearing carriage in the direction of the longitudinal axis of the screw in order to decouple the coupling, and which gearing carriage can be swiveled or can move transverse to the longitudinal axis of the screw. The gearing with the coupling can be moved away from the screw to such an extent that the screw can then be withdrawn completely from the extruder counter to the feed direction of the screw, and a screw-changing device is provided by which the existing screw of the extruder can be received and can be replaced by another screw located in the screw-changing device.

This is a U.S. national stage of application NO. PCT/DE00/03770, filedon Oct. 18, 2000. Priority is claimed on that application and on thefollowing application: Country: Germany, Application No.: 199 52 642.7,Filed: Oct. 22, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Extrusion system comprising a screw-changing device The inventionrelates to an extrusion system comprising at least one screw-typeextruder whose at least one screw is drive-connected via a coupling to agearing that is driven by a motor, said coupling being able to becoupled to and decoupled from the screw.

2. Description of the Related Art

Extrusion systems are used particularly in the plastics industry forproduction of plastic products and also for compounding of plastics,i.e. for manufacturing intermediate products made up of differentsubstances. Extrusion systems for the latter purpose are also referredto as compounding systems and in many cases have extruders with two ormore screws which mesh with one another. In these compounding systems,additives such as dyes or fiber materials, for example, are mixed intothe plastics raw material and distributed as uniformly as possibletherein. Given the wide variety of thermoplastics in particular, and thewide variety of additives, which have different material properties intheir combination, optimum production is sought by .using screws which,in their geometric configuration, are adapted as much as possible to theparticular properties of the material which is to be processed. Thereare also screws which are comparatively well suited for the processingof a relatively broad range of materials. However, this means that, inthe processing of the individual materials, such a screw or pair ofscrews generally has to operate some way from the actual operatingoptimum. This may entail a corresponding decrease in product qualityand/or a reduced production rate. In large-scale systems in particular,with high throughput rates, special screws are therefore often usedwhich are optimally suited for the processing of the particularmaterial, in other words guarantee a very high quality at a very highproduction rate.

For processing plastics batches of different materials in smallerquantities, the use of special screws for the particular materialinvolves a disproportionately high operating outlay since changing thescrews has hitherto generally required a relatively high cost,particularly in the form of the shutdown of the production plant. Inmany operations, it is therefore customary to process smaller charges ofdifferent substances on separate machines which generally have a loweroutput rate than the large-scale systems for main production quantities.These separate machines not only take up a corresponding space, but arealso in many cases characterized by a relatively low degree ofutilization. This ultimately means that the processing of smallerbatches is relatively expensive compared to the main productionquantities of the standard products.

Moreover DE 3516311 C2, which corresponds to U.S. Pat. No. 4,678,343,discloses a device with a large number of molding stations arranged on aturntable, and with a jet-molding unit which can be docked onto thesemolding stations and with which polyurethane shoe soles are injectedonto shoe uppers. The material components for the liquid polyurethaneare in this case mixed in a mixing head provided with a short mixingscrew which is mounted at one end and rotates at high speed (15000 to18000 rpm). In order to change the mixing screw, the mixing-screwbearing and drive mechanism can be drawn back by means of a hydrauliccylinder system which primarily executes the displacement movementrequired for docking the mixing head onto the molding stations, so thatthe mixing screw is withdrawn completely from the mixing head before itis decoupled from the drive mechanism and replaced with another one bymeans of a hydraulically operated screw-changing device. In the case oflonger screws, this solution would require an extremely longconstruction space. In contrast to jet-molding units, such dockingmovements are not customary in extrusion systems of the aforementionedtype and, instead, the downstream equipment remains unchanged in itsspatial arrangement with respect to the screw extruder duringproduction.

Moreover, DE 3643884 A1, which corresponds to U.S. Pat. No. 5,020,914,discloses a screw-type injection molding machine in which, by means ofan injection cylinder, the whole injection unit on a base frame of theinjection molding machine can be advanced to the injection-molding tool.To change the screw of the injection unit, the whole drive mechanism ofthe screw can be drawn a short distance back from the injection cylinderon the base frame, until the screw is decoupled from the drivemechanism. To be able to remove the screw from the screw cylinder of theinjection unit, the screw cylinder is pivoted about a vertical axis ofrotation so that the screw can be drawn past the drive mechanism in anoblique position. For pivoting of the screw cylinder, the latter isconnected to a special pivot bearing arranged for this purpose on theside.

SUMMARY OF THE INVENTION

The object of the present invention is to develop an extrusion system ofthe generic type in such a way as to substantially reduce the outlayrequired for converting the extrusion system from processing of onematerial to processing of another material with different properties.The aim therefore is to permit rapid changing of material while at thesame time maintaining a high product quality and high productivity.

For an extrusion system of the generic type, the gearing is mounted on agearing carriage configured to draw the gearing back a short distance inthe direction of the axis of the screw in order to decouple thecoupling. The carriage can be pivoted or can be moved transversely tothe axis of the screw so that the gearing with the coupling can be movedaway from the screw so that the screw can be withdrawn completely fromthe extruder counter to the feed direction of the screw. Ascrew-changing device is provided by which the existing screw of theextruder can be received and can be replaced by another screw in thescrew-changing device.

The term “gearing carriage” should not be understood here in the narrowsense that such a gearing carriage must in fact also be provided withwheels for its movement. It could also, for example, be a sled whichslides on runners in corresponding guides. However, the gearing carriageis preferably provided with rollers or wheels for its movement.

In principle, the gearing carriage could also be designed as a swivelunit so that, after the loosening of the fastening elements (e.g.screws) with which the gearing is connected securely to the extruder,said gearing with the coupling is pivoted out to the side for example,so that at the same time the coupling to the screw is decoupled and therear space for drawing the screw back counter to its feed direction ismade available. Although pivoting to the side is preferred, the pivotmovement could in principle also be upward or downward.

The gearing carriage is preferably designed such that the gearing on thegearing carriage can be drawn back in the direction of the longitudinalaxis of the screw in order thereby to disconnect the coupling of thescrew. The gearing carriage itself can expediently be moved transverseto the longitudinal axis of the screw. To permit disconnection of thecoupling, the gearing carriage can be equipped for example with a smallsled whose runners extend parallel to the feed direction of the screw.The two movements for disconnecting the coupling and for moving thegearing away, with the drive motor flange-mounted thereon, could inprinciple also be made possible by providing the gearing carriage withwheels, for example guidable wheels.

The screw-changing device for mechanized exchange of the screw can bedesigned as a stationary or movable screw magazine, with a maneuveringdevice for withdrawal and insertion of a screw. In the simplest case,the screw magazine is designed with a rotatable double arm, where onearm is intended to receive the screw to be replaced, and the other armcarries the new screw. The screw magazine is preferably configured as arevolver magazine or paternoster magazine and is thus suited to receivea large number of replacement screws. This ensures a high degree offlexibility in terms of the processing of a correspondingly large numberof different materials.

The maneuvering device for removing and inserting a screw is preferablya linearly movable slide with a gripping device for connection to theparticular screw.

In principle it is possible for the movements of the gearing carriageand of the maneuvering device to be executed by an operator. In thiscase, the configuration of the extrusion system according to theinvention relieves the operator at least from the heavy work duringdismantling of the old screw and fitting of the new screw. In addition,the necessary movements of the screws can take place in set tracks, sothat the time needed for screw-changing is considerably reduced.

Still greater time savings can be made if the gearing carriage and ifappropriate also the screw-changing device are each provided with amotor drive. This drive is preferably actuated by an electronic controlmeans whose program memory is preferably set up for fully automaticscrew-changing.

A particularly significant saving is achieved if an extrusion systemequipped with twin-screw extruders is designed in accordance with theinvention, in which case the screw-changing device is set up forscrew-changing in pairs. Such extrusion systems are particularlyadvantageous as compounding systems for processing of thermoplastics.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in greater detail below on the basis of theillustrative embodiment which is shown in highly schematic form in thesingle figure.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

An extruder 1 which is designed as a single-screw extruder and whosedownstream equipment is not shown here has a gearing 2 at its end remotefrom the extruder head, and a motor 3 is flange-mounted onto thisgearing 2 in order to drive the extruder screw. The gearing 2, whoseworking position is indicated by broken lines in the figure, is equippedwith a coupling (not shown) for attachment of the upstream end of theextruder screw. The gearing 2, with the motor 3 flange-mounted thereon,is mounted on a gearing carriage (of which no details are shown here).To disconnect the coupling of the gearing 2 from an extruder screw stillpresent in the extruder 1, the gearing carriage can be drawn back ashort distance counter to the feed direction of the extruder screw, forexample after releasing a quick-action clamp with which the gearing 2 isconnected securely to the extruder 1 during normal system operation.This decoupling path has been indicated by reference number 11 in thefigure. After the extruder screw and the coupling have been separatedfrom one another, the gearing carriage in the example shown is moved ashort distance to the right, transverse to the feed direction of theextruder 1, so that the rearward space on the extruder 1 is free forscrew-changing. The path of movement for screw-changing has beendesignated by reference number 10. The gearing 2 and the motor 3flange-mounted thereon have been shown in the screw-changing position bymeans of solid lines, to distinguish this from the operating positionshown in broken lines. In the screw-changing position, the gearing isindicated by reference number 5 and the motor by reference number 6.After the screw-changing position has been reached, the screw 4 of theextruder 1 can be withdrawn from the extruder 1 by means of amaneuvering device 8. It is held by a holder on a screw-changing device9. This holder is designed for example as a two-arm pivot arm. Mountedon the other arm of this two-arm pivot arm there is another screw 7which is to take the place of the screw 4 which has previously been inuse. To do this, the maneuvering device 8 is released from the screw 4and moved slightly farther back. The two-arm pivot arm is then turned sothat the screw 7 comes into the position of the screw 4. By renewedactuation of the maneuvering device 8, the new screw 7 is then grippedand pushed into the extruder 1. After the maneuvering device 8 has beenreleased from the screw 7 and drawn back, the gearing carriage with thegearing and the motor is then moved from the screw-changing positionindicated by 5 and 6 back into the position 2, 3 shown by broken lines,that is to say is first displaced back toward the left by thedisplacement path 10 and then pushed back along the decoupling path 11to the replacement screw 7 situated in the extruder 1, so that thecoupling of the gearing 2 connects up to the new screw 7. In a preferredembodiment of the invention, the movements of the gearing carriage andof the screw-changing device 9 and maneuvering device 8 are effected bymotor drives which are controlled by a programmable electronic controlmeans (not shown). Since screw-changing can in this way be donepractically without any intervention by personnel and in an extremelyshort time, there are only very brief shutdown times for the wholesystem and, as a consequence of this, considerably lower shutdown coststhan was previously the case. In this way, it is economically feasiblealso to process smaller batches of plastics using a large-scale,high-performance extrusion system. This permits production ofhigh-quality products at low costs and in small quantities.

The gearing carriage, which is indicated as a unit with the gearing 5,is mounted to the extruder frame for movement parallel and orthogonal tothe axis of the extruder screw, or alternatively parallel and thenpivoting so that the gearing with the coupling moves away the screw.

What is claimed is:
 1. An extrusion system comprising a screw typeextruder having at least one screw with a longitudinal axis, said screwbeing rotatable about said axis to extrude material in a feed direction,a gearing drive-connected to said screw via a coupling which can becoupled to and decoupled from said screw, a motor for driving saidgearing, a gearing carriage on which said gearing is mounted, saidgearing carriage being movable so that the gearing with the coupling canmoved away from the screw so that the screw can be withdrawn from theextruder counter to the feed direction of the screw, and a screwchanging device which receives said screw from said extruder and carriesanother screw for replacing said screw received from said extruder. 2.An extrusion system as in claim 1, wherein said screw changing devicecomprises a movable screw magazine and a maneuvering device for removingand inserting a screw.
 3. An extrusion system as in claim 2 wherein saidscrew magazine is one of a revolver magazine and a paternoster magazine.4. An extrusion system as in claim 1 wherein said gearing carriage canbe drawn back in the direction of the longitudinal axis of the screw inorder to decouple the coupling from the screw.
 5. An extrusion system asin claim 4 wherein said gearing carriage can pivot so that the gearingcan move away from the longitudinal axis of the screw.
 6. An extrusionsystem as in claim 4 wherein said gearing carriage can move transverselyto the longitudinal axis of the screw.
 7. An extrusion system as inclaim 1 further comprising a motor for decoupling said coupling fromsaid screw.
 8. An extrusion system as in claim 1 further comprising amotor for moving said gearing carriage.
 9. An extrusion system as inclaim 1 further comprising a motor for moving said screw changingdevice.
 10. An extrusion system as in claim 1 further comprising anelectronic controller for actuating movement of at least one of saidcoupling, said gearing carriage, and said screw changing device.
 11. Anextrusion system as in claim 10 wherein said electronic controllercomprises a program memory which is set up for automatic screw changing.12. An extrusion system as in claim 1 wherein said extruder is a twinscrew extruder having a pair of screws, said screw changing device beingset up for changing the screws in pairs.
 13. An extrusion system as inclaim 1 wherein said extrusion system is a compounding system forprocessing thermoplastics.